U.S. patent application number 13/439934 was filed with the patent office on 2013-10-10 for systems and methods for performing industrial processes that generate pyrophoric particles.
The applicant listed for this patent is Jeffrey W. Austin, Scott L. Fitzner, Jeffrey T. Lee, Roger D. Ridgeway. Invention is credited to Jeffrey W. Austin, Scott L. Fitzner, Jeffrey T. Lee, Roger D. Ridgeway.
Application Number | 20130263737 13/439934 |
Document ID | / |
Family ID | 49291271 |
Filed Date | 2013-10-10 |
United States Patent
Application |
20130263737 |
Kind Code |
A1 |
Lee; Jeffrey T. ; et
al. |
October 10, 2013 |
SYSTEMS AND METHODS FOR PERFORMING INDUSTRIAL PROCESSES THAT
GENERATE PYROPHORIC PARTICLES
Abstract
A process chamber is configured to contain a work piece in a
controlled atmosphere and to perform a process that emits
pyrophoric particulates. A closed recirculating loop connected with
the process chamber recirculates gas defining the controlled
atmosphere through the process chamber. A filter in the closed
recirculating loop captures the generated pyrophoric particulates
in the recirculating gas. A valve set has a work configuration
defining the closed recirculating loop including the connection of
the process chamber with the filter, and a filter regeneration
configuration in which the filter is blocked off from the process
chamber and is connected with an exhaust. A work piece is loaded
into the process chamber. With the valve set in the work
configuration, the process is performed on the loaded work piece.
Thereafter, regeneration gas containing oxygen is delivered to the
filter with the valve set in the regeneration configuration.
Inventors: |
Lee; Jeffrey T.; (Forest,
VA) ; Ridgeway; Roger D.; (Lynchburg, VA) ;
Austin; Jeffrey W.; (Evington, VA) ; Fitzner; Scott
L.; (Appomattox, VA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Lee; Jeffrey T.
Ridgeway; Roger D.
Austin; Jeffrey W.
Fitzner; Scott L. |
Forest
Lynchburg
Evington
Appomattox |
VA
VA
VA
VA |
US
US
US
US |
|
|
Family ID: |
49291271 |
Appl. No.: |
13/439934 |
Filed: |
April 5, 2012 |
Current U.S.
Class: |
95/279 ;
55/302 |
Current CPC
Class: |
B01D 46/42 20130101;
B01D 46/006 20130101 |
Class at
Publication: |
95/279 ;
55/302 |
International
Class: |
B01D 46/42 20060101
B01D046/42 |
Claims
1. An apparatus comprising: a process chamber configured to contain
a work piece in a controlled atmosphere and to perform a process on
the work piece in the process chamber that emits pyrophoric
particulates into the controlled atmosphere; a closed recirculating
loop connected with the process chamber to recirculate gas defining
the controlled atmosphere through the process chamber; a filter
disposed in the closed recirculating loop and configured to capture
the generated pyrophoric particulates in the recirculating gas; and
a valve set configured to have (1) a work configuration defining
the closed recirculating loop including the connection of the
process chamber with the filter and (2) a filter regeneration
configuration in which the filter is blocked off from the process
chamber and is connected with an exhaust.
2. The apparatus of claim 1, further comprising: An exhaust filter
arranged to filter gas discharged at the exhaust.
3. The apparatus of claim 1, further comprising: a regeneration gas
source delivering regeneration gas containing oxygen; wherein the
working configuration of the valve set blocks the regeneration gas
source from the closed recirculating loop; and wherein the valve
set in the filter regeneration configuration also connects the
regeneration gas source to the filter to flow regeneration gas
through the filter.
4. The apparatus of claim 3, wherein the regeneration gas source
delivers compressed air.
5. The apparatus of claim 3, wherein the regeneration gas source
delivers regeneration gas comprising greater than 22% oxygen.
6. The apparatus of claim 1, wherein the gas defining the
controlled atmosphere is argon.
7. The apparatus of claim 1, wherein the gas defining the
controlled atmosphere is an inert gas.
8. The apparatus of claim 1, wherein the filter comprises: at least
one metallic filter plate.
9. The apparatus of claim 1, further comprising: an ignition source
arranged to ignite pyrophoric particulates captured by the
filter.
10. The apparatus of claim 1, wherein the process chamber is
configured at least by including an optical port to perform a laser
welding process on the work piece in the process chamber, and the
apparatus further comprises: a welding laser arranged to perform
laser welding on the work piece through the optical port.
11. A method performed using the apparatus of claim 1, the method
comprising: (i) loading a work piece into the process chamber; (ii)
with the valve set in the work configuration, performing the
process on the loaded work piece that emits pyrophoric particulates
into the controlled atmosphere; and (iii) after performing
operation (ii), delivering regeneration gas containing oxygen to
the filter with the valve set in the regeneration
configuration.
12. The method of claim 11, wherein operations (i) and (ii) are
repeated more than once before performing the operation (iii).
13. The method of claim 11, further comprising: evacuating the
controlled atmosphere from the process chamber after performing
operation (ii) and before performing operation (iii).
14. The method of claim 11, wherein: operation (i) comprises
loading a work piece comprising a zirconium alloy into the process
chamber; and operation (ii) comprises performing laser welding of
the work piece.
15. The method of claim 11, wherein: operation (i) comprises
loading a work piece comprising interlocked zirconium alloy straps
into the process chamber; and operation (ii) comprises laser
welding the interlocked zirconium alloy straps together to
construct a nuclear fuel assembly spacer grid component.
16. The method of claim 11, wherein: operation (i) comprises
loading a work piece comprising interlocked metal straps into the
process chamber; and operation (ii) comprises laser welding the
interlocked metal straps together to construct a nuclear fuel
assembly spacer grid component wherein during the laser welding the
metal straps emit pyrophoric particulates into the controlled
atmosphere.
17. A method comprising: performing a process on a work piece
wherein the process emits pyrophoric particulates into a controlled
atmosphere contained in a process chamber; during the performing of
the process, recirculating a gas defining the controlled atmosphere
through (i) the process chamber and (ii) a filter configured to
capture the pyrophoric particulates; and after performing the
process, regenerating the filter by flowing regeneration gas
including oxygen through the filter.
18. The method of claim 17, wherein the filter has an inlet side
that receives gas discharged from the process chamber by the
recirculating and a discharge side, and the regenerating comprises:
flowing regeneration gas including oxygen into the discharge side
of the filter.
19. The method of claim 17, wherein the controlled atmosphere is
argon.
20. The method of claim 17, wherein the controlled atmosphere is an
inert atmosphere.
21. The method of claim 17, further comprising: after performing
the process but before regenerating the filter, evacuating the
controlled atmosphere from the process chamber.
22. The method of claim 17, further comprising: repeating the
process, including the recirculating, on a plurality of work pieces
before regenerating the filter.
23. The method of claim 17, wherein the regenerating further
comprises: while flowing regeneration gas including oxygen through
the filter, activating an ignition source to ignite pyrophoric
particles captured by the filter.
24. The method of claim 17, wherein the process comprises laser
welding.
25. The method of claim 24, wherein the work piece comprises an
interlocked array of metal straps and the laser welding constructs
a nuclear fuel assembly spacer grid component.
26. An apparatus comprising: a process chamber configured to
contain a work piece in a controlled atmosphere and to perform a
process on the work piece in the process chamber that emits
pyrophoric particulates into the controlled atmosphere; a closed
recirculating loop connected with the process chamber to
recirculate gas defining the controlled atmosphere through the
process chamber; a filter disposed in the closed recirculating loop
and configured to capture the generated pyrophoric particulates in
the recirculating gas wherein the filter has an inlet side
receiving gas flowing from the process chamber and a discharge
side; and a valve set configured to have (1) a work configuration
defining the closed recirculating loop including the connection of
the process chamber with the inlet side of the filter and (2) a
filter regeneration configuration in which the inlet side of the
filter is blocked off from the process chamber and is connected
with an exhaust.
27. The apparatus of claim 26, further comprising: a regeneration
gas source delivering regeneration gas containing oxygen; wherein
the working configuration of the valve set blocks the regeneration
gas source from the closed recirculating loop; and wherein the
valve set in the filter regeneration configuration also connects
the regeneration gas source to the outlet side of the filter to
flow regeneration gas into the discharge side of the filter.
28. The apparatus of claim 26, wherein the filter comprises: at
least one metallic filter plate.
29. The apparatus of claim 28, wherein the at least one metallic
filter plate includes a metallic filter plate having a pore size of
0.2 micron or smaller.
30. The apparatus of claim 28, wherein the at least one metallic
filter plate includes a metallic filter plate having a pore size of
0.5 micron or smaller.
31. The apparatus of claim 28, wherein the at least one metallic
filter plate includes a metallic filter plate having a pore size of
1.0 micron or smaller.
32. The apparatus of claim 28, wherein the at least one metallic
filter plate includes a metallic filter plate having a pore size of
2.0 micron or smaller.
33. The apparatus of claim 26, wherein the valve set further has
(3) an evacuation configuration in which a vacuum line draws the
controlled atmosphere from the discharge side of the filter.
34. A method performed using the apparatus of claim 26, the method
comprising: (i) loading a work piece into the process chamber; (ii)
with the valve set in the work configuration, performing the
process on the work piece loaded in the process chamber that emits
pyrophoric particulates into the controlled atmosphere; and (iii)
after performing operation (ii), delivering regeneration gas
containing oxygen to the discharge side of the filter with the
valve set in the regeneration configuration.
Description
BACKGROUND
[0001] The following relates to the industrial processing arts,
industrial safety arts, controlled atmosphere processing arts, and
related arts.
[0002] Certain types of industrial processes generate pyrophoric
particles. For example, in the nuclear power industry, some
components are selected to be constructed of zirconium alloy
material due in part to low neutron absorption characteristics of
these alloys. However, high temperature processes such as welding,
cutting, and so forth applied to zirconium alloy material can not
only be corrosive to material performance if done in an oxygen
environment but further tend to generate zirconium alloy
particulates regardless of fabrication environment. In an oxygen
environment the higher surface area-to-volume ratio of these
particulates compared with the bulk material enhances their
oxidation characteristics to a point where these particulates
become flammable and can spontaneously combust in air or in
response to a spark or other ignition source. Accordingly, for
these and other reasons such processing is typically performed in
an inert atmosphere such as an argon atmosphere. However, the
generated pyrophoric particulates must still be dealt with.
[0003] Historically, the process exhaust was vented to atmosphere.
An ignition source might be included in the chimney or vent to
encourage burning of any pyrophoric particles. However, airborne
metallic particulates can cause respiratory problems and raise
other environmental concerns. Accordingly, modern processing
methodologies filter out the metallic particulates, including
pyrophoric particulates, from the exhaust stream prior to
exhausting to atmosphere.
[0004] The filtering of metallic particulates is performed using
wet scrubbers and/or dry filters. In the case of zirconium alloy
processing a conventional approach is to employ a wet scrubber to
capture most pyrophoric particles, followed by a dry filter for
final cleanup prior to exhausting to atmosphere. However, in
processes that generate high concentrations of very small
pyrophoric particulates, the wet scrubbers are not highly
effective. For example, in some zirconium alloy processes greater
than 50% of the pyrophoric particulates are smaller than 1 micron
in diameter, and these small particulates are not effectively
removed by the wet scrubber. In such cases, the dry filter
accumulates pyrophoric particulates rapidly, and must be replaced
on a frequent basis--failure to do so can result in spontaneous
combustion of pyrophoric particulates in the dry filter and
possible fire and/or explosion.
BRIEF SUMMARY
[0005] In one aspect of the disclosure, an apparatus comprises: a
process chamber configured to contain a work piece in a controlled
atmosphere and to perform a process on the work piece in the
process chamber that emits pyrophoric particulates into the
controlled atmosphere; a closed recirculating loop connected with
the process chamber to recirculate gas defining the controlled
atmosphere through the process chamber; a filter disposed in the
closed recirculating loop and configured to capture the generated
pyrophoric particulates in the recirculating gas; and a valve set
configured to have (1) a work configuration defining the closed
recirculating loop including the connection of the process chamber
with the filter and (2) a filter regeneration configuration in
which the filter is blocked off from the process chamber and is
connected with an exhaust.
[0006] In another aspect of the disclosure, a method is performed
using the apparatus of the immediately preceding paragraph. The
method comprises: (i) loading a work piece into the process
chamber; (ii) with the valve set in the work configuration,
performing the process on the loaded work piece that emits
pyrophoric particulates into the controlled atmosphere; and (iii)
after performing operation (ii), delivering regeneration gas
containing oxygen to the filter with the valve set in the
regeneration configuration.
[0007] In another aspect of the disclosure, a method is disclosed.
A process is performed on a work piece. The process emits
pyrophoric particulates into a controlled atmosphere contained in a
process chamber. During the performing of the process, a gas
defining the controlled atmosphere is recirculated through (i) the
process chamber and (ii) a filter configured to capture the
pyrophoric particulates. After performing the process, the filter
is regenerated by flowing regeneration gas including oxygen through
the filter.
[0008] In another aspect of the disclosure, an apparatus comprises:
a process chamber configured to contain a work piece in a
controlled atmosphere and to perform a process on the work piece in
the process chamber that emits pyrophoric particulates into the
controlled atmosphere; a closed recirculating loop connected with
the process chamber to recirculate gas defining the controlled
atmosphere through the process chamber; a filter disposed in the
closed recirculating loop and configured to capture the generated
pyrophoric particulates in the recirculating gas wherein the filter
has an inlet side receiving gas flowing from the process chamber
and a discharge side; and a valve set configured to have (1) a work
configuration defining the closed recirculating loop including the
connection of the process chamber with the inlet side of the filter
and (2) a filter regeneration configuration in which the inlet side
of the filter is blocked off from the process chamber and is
connected with an exhaust.
[0009] In another aspect of the disclosure, a method is performed
using the apparatus of the immediately preceding paragraph. The
method comprises: (i) loading a work piece into the process
chamber; (ii) with the valve set in the work configuration,
performing the process on the work piece loaded in the process
chamber that emits pyrophoric particulates into the controlled
atmosphere; and (iii) after performing operation (ii), delivering
regeneration gas containing oxygen to the discharge side of the
filter with the valve set in the regeneration configuration.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The invention may take form in various components and
arrangements of components, and in various process operations and
arrangements of process operations. The drawings are only for
purposes of illustrating preferred embodiments and are not to be
construed as limiting the invention.
[0011] FIGS. 1-3 diagrammatically show diagrammatic representations
of a welding system employs recirculating argon in the welding of
zirconium alloy components, where:
[0012] FIG. 1 shows the system in the welding configuration;
[0013] FIG. 2 shows the system set for argon evacuation; and
[0014] FIG. 3 shows the system in a filter regeneration
configuration.
[0015] FIG. 4 diagrammatically shows a welding process suitably
performed by the welding system of FIGS. 1-3.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0016] With reference to FIG. 1, an illustrative welding system for
performing welding of zirconium alloy components is shown. The
welding system may, by illustrative example, be used to weld an
interlocked assembly of zirconium alloy straps in order to
construct a nuclear fuel assembly spacer grid component. In this
illustrative example, an interlocked assembly of zirconium alloy
straps 8 (shown in an inset perspective view only in FIG. 1)
defines a zirconium alloy work piece 10 that is placed into a
welding chamber 12. (Alternatively, the metal straps may be made of
a material other than a zirconium alloy, such as steel or Inconel).
This illustrative embodiment is configured to perform laser
welding--for this purpose, the welding chamber 12 includes a window
14 of glass or another material that is transparent to light
generated by a welding laser source 16. (It is to be appreciated
that the term "light" as used here may encompass electromagnetic
radiation outside of the visible spectrum, such as ultraviolet
light or infrared light). The welding chamber 12 is sufficiently
airtight to enable it to be filled with an inert gas such as argon
during processing of the work piece 10 without having unacceptable
leakage of argon during the processing. Typically, the welding
chamber 12 is sufficiently airtight that it can be evacuated to a
pressure of less than 50 mTorr, and more preferably less than 10
mTorr, and in some embodiments 1 mTorr or lower, using a mechanical
vacuum pump; however, a more leaky (or less) chamber is also
contemplated.
[0017] More generally, the work piece may be any work piece whose
processing by the system generates pyrophoric particles. For
example, the work piece may be a zirconium alloy blank that is to
be cut, grinded, polished, or otherwise processed to form a desired
component using a cutting, grinding, polishing, or other process
that generates pyrophoric zirconium alloy particulates. Other
materials that tend to generate pyrophoric particulates under
processing include magnesium, titanium, hafnium, zinc, uranium,
thorium, various alloys of the foregoing, and so forth. Depending
upon the type of processing, materials such as steel may also
generate pyrophoric particulates, especially when the processing
produces very small-diameter particulates having high surface
area-to-volume ratios. Process parameters such as exhaust
temperature and chemical composition can also impact the whether
the generated particulates are pyrophoric in the exhaust
environment. Moreover, in some processes the pyrophoric
particulates may be generated from abrasives or other components,
other than the work piece, that are used in the process.
[0018] The welding chamber 12 may, in more general terms, be any
process chamber in which a work piece undergoes a process that
generates pyrophoric particulates. In non-optical processes such as
mechanical cutting or grinding, the window 14 may be omitted (or,
alternatively, may be retained in order to allow visual monitoring
of the process). Although not shown in FIG. 1, the process chamber
12 includes a sealable door for introducing the work piece and
removing it after the process is complete. Alternatively, a load
lock can be used for this purpose so as to load and unload work
pieces without evacuating the argon or other inert atmosphere. In
the case of mechanical cutting or grinding, the chamber is
configured to perform the process by including suitable robotic
cutting or grinding implements inside the process chamber.
[0019] The process which generates pyrophoric particles is
performed in a controlled atmosphere in which the oxygen level is
too low for the pyrophoric particulates to oxidize. Typically, an
inert atmosphere comprising a gas such as argon is used. Nitrogen
is also an option for some processes--however, zirconium alloys
tend to detrimentally interact with nitrogen. It is also
contemplated for the controlled atmosphere to be at a pressure
other than atmospheric pressure, and/or to have a specified flow
rate. (For example, in laser welding applications a high flow rate
can reduce buildup of fumes on the optical window 14 and consequent
partial occusion of the laser beam). Before beginning the process,
the chamber 12 is evacuated and filled with the controlled
atmosphere (e.g., filled with argon in the instant example). In the
illustrative system of FIGS. 1-3, a single pipe or tube 20 is
selectively connected with a vacuum pump or house vacuum (not
shown) or with a gas cylinder or other source of the argon or other
gas that makes up the controlled atmosphere (also not shown).
Alternatively, separate vacuum and gas inlet lines may be provided.
Optionally, the evacuation/fill operations are repeated one or more
times to provide more complete removal of residual oxygen.
[0020] The disclosed process systems employ recirculation of the
controlled atmosphere through a closed recirculation loop that is
connected with the process chamber 12 and includes a filter 22
configured to capture the generated pyrophoric particulates in the
recirculating gas defining the controlled atmosphere (e.g., argon
gas). The closed recirculation loop of the illustrative embodiment
of FIG. 1 includes a filter housing 24 containing the filter 22, a
blower or pump 26 for driving the recirculation of the gas (e.g.,
argon) defining the controlled atmosphere, a pipe or tube 28
running from the process chamber 12 to the filter housing 24, and a
pipe or tube 30 running from the filter housing 24 back to the
process chamber 12. As seen in FIGS. 1-3, the blower or pump 26 is
mounted on or operatively engages with the pipe or tube 30. The
blower or pump 26 is arranged to drive the gas (e.g., argon)
defining the controlled atmosphere in the direction in which the
gas discharged from the process chamber 12 into the pipe 28 flows
to the filter housing 24 and into an inlet side 32 of the filter
22. The gas is filtered by the filter 22 and discharges at a
discharge side 34 of the filter 22, and then flows via pipe 30 back
to the process chamber 12. (In the illustrative system
representation shown in FIG. 1, the flow of argon gas is
counter-clockwise).
[0021] The system further includes components for regenerating the
filter 22, including a regeneration gas source 40 delivering
regeneration gas containing oxygen to the discharge side 34 of the
filter 22, and an exhaust 42 which in the illustrative embodiment
includes an exhaust filter 44. The regeneration gas may be
compressed air, which typically includes 21% oxygen, 78% nitrogen
and 1% "other gases". Alternatively, the regeneration gas may be
regeneration gas comprising greater than 22% oxygen, such as an
air/O.sub.2 mixture.
[0022] The system further includes a valve set, which in the
illustrative embodiment includes: a valve V1 that opens or closes
the combined vacuum/argon line 20; a valve V2 that selectively
closes the pipe or tube 28 to isolate the discharge of the process
chamber 12 from the filter housing 24; a valve V3 that selectively
opens or closes the pipe 30 running from the filter housing 24 back
to the process chamber 12; a valve V4 that selectively connects the
regeneration gas source 40 to the discharge side 34 of the filter
22; and a valve V5 that selectively connects the inlet side 32 of
the filter 22 with the exhaust 42. Note that in the diagrammatic
system representations of FIGS. 1-3, valves are shown only when
they are in the closed position. FIG. 1 shows a work configuration
of the valve set in which only valves V1, V4, V5 are closed; valves
V2, V3 are open to form the closed recirculating loop and hence are
not shown. FIG. 2 shows an evacuation configuration in which valves
V2, V4, V5 are closed and valves V1, V3 are open and hence not
shown. FIG. 3 shows a filter regeneration configuration in which
valves V1, V2, V3 are closed and valves V4, V5 are open and hence
not shown. A valve set controller 46 is optionally provided to
automatically open and close valves of the valve set to achieve the
various working, evacuation, and filter regeneration configurations
shown in FIGS. 1-3, respectively. Alternatively, the valves of the
valve set can be manually operated. If provided, the valve set
controller 46 is operatively connected with the various valves V1,
V2, V3, V4, V5 by suitable electrical, pneumatic, or other
actuation lines (not shown), or alternatively employs wireless
communication with local valve controller units disposed with the
individual valves.
[0023] In the following, operation of the system is described in
greater detail. In overview, the welding process (or, more
generally, the process that emits pyrophoric particulates into the
controlled atmosphere) is performed using the working configuration
shown in FIG. 1. In this configuration the gas (e.g. argon)
defining the controlled atmosphere is recirculated through the
process chamber 12. After the process is complete, the controlled
atmosphere is removed using the evacuation configuration shown in
FIG. 2, and then the filter 22 is regenerated using the filter
regeneration configuration shown in FIG. 3.
[0024] With particular reference to FIG. 1, once the gas fill
operation is complete the valve V1 is closed to seal off the
process chamber 12. (As previously noted, this preparatory phase
may optionally include multiple evacuation/fill operations to more
completely remove residual oxygen). FIG. 1 shows the working
configuration with the valve V1 closed. The valves V2, V3 are open
(and hence not shown in FIG. 1) in order to form the closed
recirculation loop running from the discharge of the process
chamber 12 through pipe 28, filter housing 24, and pipe 30 back to
the process chamber 12. Valve V4 is closed to disconnect the
regeneration gas source 40 from the filter housing 24, and valve V5
is closed to disconnect the exhaust 42 from the filter housing 24.
The blower or pump 26 is operating in the working configuration to
drive recirculation of the gas (e.g., argon) defining the
controlled atmosphere. Because the valve V1 is closed, there is no
inflow of argon into the system--rather, a fixed quantity of argon
is recirculating through the system. Alternatively, V1 may remain
slightly open to permit a small flow of the gas (e.g., argon) into
the system thereby maintaining system pressure above atmospheric
and inhibiting the atmosphere surrounding the system from leaking
therein. In this manner, any leakage of the closed recirculating
loop is leakage of the inert atmosphere out such that oxygen in the
atmosphere does not leak in and contaminate the welding
environment. The process (e.g., illustrative laser welding of the
spacer grid) is performed, as diagrammatically indicated in FIG. 1
by illustrating the laser beam 48 in FIG. 1. The process injects
pyrophoric particulates into the controlled atmosphere in the
process chamber 12. The recirculating flow of the controlled
atmosphere drives these pyrophoric particulates through the pipe 28
to the inlet side 32 of the filter 22, where the particulates are
trapped or captured by the filter 22. In general, the filter 22
should be capable of capturing particles of the expected size of
the pyrophoric particles, and should be capable of withstanding
substantial heating (since the filter regeneration, to be
described, entails heating). In some suitable embodiments, the
filter 22 comprises at least one metallic filter plate. The pore
size of the filter plate or plates depends upon the expected
pyrophoric particulate size, which in turn depends upon the aspects
such as the process being performed in the process chamber 12, the
material and other characteristics of the work piece 10, and so
forth.
[0025] In some embodiments, the at least one metallic filter plate
includes a metallic filter plate having a pore size of 0.2 micron
or smaller. In some embodiments, the at least one metallic filter
plate includes a metallic filter plate having a pore size of 0.5
micron or smaller. In some embodiments, the at least one metallic
filter plate includes a metallic filter plate having a pore size of
1.0 micron or smaller. In some embodiments, the at least one
metallic filter plate includes a metallic filter plate having a
pore size of 2.0 micron or smaller. In some embodiments multiple
filter plates may be used. For example, the multiple filter plates
may have successively smaller pore sizes in order to distribute the
captive pyrophoric particulates over several filter plates (i.e.,
the largest particulates are caught by the first, largest-pore size
plate, the next-largest particulates are caught by the second,
somewhat smaller-pore size plate, and so forth until the smallest
particulates are caught by the last, smallest-pore size plate).
Instead of or in addition to metallic filter plates with discrete
pores of uniform size, other filter configurations can be employed,
such as one or more filter plates having a High-Efficiency
Particulate Air (HEPA) filter type made up of interweaved metallic
fibers. Another contemplated approach is use of an electrostatic
filter as at least one component of the filter 22.
[0026] After the process that generates pyrophoric particulates is
complete (e.g., after the laser welding is complete), the system is
switched to the evacuation configuration shown in FIG. 2. This is
done by closing the valve V2 to isolate the discharge of the
process chamber 12 from the inlet side 32 of the filter 22 and
opening the valve V1 with the tube or pipe 20 connected to a vacuum
pump or house vacuum. The controlled atmosphere (e.g., argon) is
evacuated via the pipe 20. Because valve V2 is closed, any suction
applied to the filter 22 is applied through the pipe 30 to the
discharge side 34 of the pipe. This is advantageous because it
reduces the likelihood of a "reverse" flow (i.e. flow from filter
discharge side 34 to filter inlet side 32) causing the dislodgement
of captured pyrophoric particulates. The blower or pump 26 is
typically turned off during the evacuation; alternatively, it may
be left on to drive gas toward the vacuum pipe 20.
[0027] After the controlled atmosphere has been evacuated, the
system is switched to the filter regeneration configuration shown
in FIG. 3 by closing the valve V1 to switch out the vacuum/argon
line 20, keeping valve V2 closed and closing valve V3 to isolate
the filter housing 24, opening valve V4 to apply the regeneration
gas to the discharge side 34 of the filter 22, and opening valve V5
to provide an exhaust path to the exhaust 42. The regeneration gas
supplied by the regeneration gas source 40 contains oxygen. When
the pyrophoric particles trapped by the filter 22 are exposed to
the oxygen, they spontaneously oxidize and burn. Additionally or
alternatively, a spark or flame may be applied by an ignition
source 50 mounted on the filter 22 (as shown) or inside the filter
housing 24 to induce combustion thereby ensuring the oxidation of
the particles. The air flow produced by the flow of regeneration
gas, in combination with forces generated by the combustion of the
pyrophoric particulates, releases the particulates (or pieces
thereof resulting from the combustion) from the filter 22 where
they flow to the exhaust 42. In the illustrative example, these
particulates (which are no longer pyrophoric since they have
already undergone oxidation) are captured by the particulate
exhaust filter 44; alternatively, the exhaust may flow into a
scrubber system or other further processing components. As another
alternative, the combusted particulates may be directly exhausted
to atmosphere without going through the exhaust filter 44 if the
combusted particulates are environmentally benign.
[0028] After filter regeneration is complete, the system is
returned to the work configuration (FIG. 1), and the process
chamber 12 is vented (e.g., via a vent valve, not shown) and the
work piece loading door (not shown) is opened and the work piece 10
is removed and, if desired, a new work piece is loaded and the
process is repeated.
[0029] The filter regeneration (FIG. 3) should be performed before
the concentration of pyrophoric particulates on or in the filter 22
becomes high enough to risk a substantial auto-ignition during the
work piece loading process (i.e., when the filter housing 24 is
filled with air). In some embodiments, this may entail performing
filter regeneration after each work piece is processed. On the
other hand, if the pyrophoric particulate generation rate is low
enough, it may be possible to perform processing on two, three, or
more work pieces before performing filter regeneration. The
decision of when to perform filter regeneration can be based on
various informational sources. In an "open-loop" approach, the
regeneration is done on a fixed cycle (e.g., after every three work
pieces are processed, by way of illustrative example).
Alternatively, it is contemplated to employ some sort of sensor
that measures a signal indicative of the particulate load that the
filter 22 is holding. In illustrative FIGS. 1-3, a flow or pressure
sensor 52 at the inlet of the blower or pump 26 measures the flow
or pressure at that inlet; from this value (and, possibly, also
based on a motor current or other metric of the "effort" being
expended by the blower 26), the flow resistance being imposed by
the filter 22 can be estimated, and this is indicative of the
particulate load on the filter 22. (That is, higher particulate
load introduces more flow resistance).
[0030] As noted previously, the valve set V1, V2, V3, V4, V5 is
optionally automatically controlled by a valve set controller 46.
To further automate the system, this controller 46 optionally also
operates the ignition source 50 (if included) during filter
regeneration, and may optionally monitor the sensor 52 or other
metrics to determine when filter regeneration should be performed.
The controller 46 may also read a sensor or sensors such as a
filter temperature sensor (not shown) to monitor the filter
regeneration process and terminate filter regeneration at an
appropriate point. (In this example, filter regeneration is
suitably detected as being initiated when the filter temperature
goes up, indicating combustion of the pyrophoric particulates has
started. The filter regeneration terminates when the temperature
drops back down below a threshold indicating that the combustion is
substantially complete. The ignition source 50, if available, may
also be re-activated after the temperature drops back to ensure
that no particulate clumps remain to be burned off.)
[0031] With reference to FIG. 4, the overall process is summarized.
In an operation 60, the work piece 10 is loaded into the process
chamber 12. If the work piece is loaded via a door, this entails
venting the chamber 12 to atmosphere via a suitable vent valve (not
shown) and opening the chamber, and after loading the process
chamber 12 is evacuated and backfilled with argon (again, this
evacuation/fill processing is optionally repeated). Alternatively,
if a load lock is provided then the work piece is loaded into the
load lock which is then pumped down using a vacuum pump or house
vacuum followed by opening a gate valve to transfer the work piece
from the load lock into the process chamber 12. In this case the
backfill operation 62 may be omitted or may be limited to a partial
fill to replace any argon volume lost to the load lock. In an
operation 64, the laser welding process is performed as described
with reference to FIG. 1. In an operation 66, the process chamber
12 is evacuated as described with reference to FIG. 2. In an
operation 70 it is decided whether filter regeneration should be
performed. If no, then process returns to operation 60 to remove
the completed work piece and to load a new work piece is one is
queued for processing. On the other hand, if filter regeneration is
to be performed then the filter regeneration operation 72 is
performed as described with reference to FIG. 3, followed by return
to operation 60 to remove the completed work piece and to load a
new work piece is one is queued for processing.
[0032] The laser welding process described with reference to FIGS.
1-4 is merely illustrative, and numerous variations are
contemplated. For example, different valve sets can be used to
implement the various work, evacuation, and filter regeneration
configurations. For example, if separate vacuum and argon lines are
provided then the valve V1 is suitably replaced by separate valves
for the vacuum and argon lines. Moreover, these lines may be
located elsewhere than being directly connected with the process
chamber. For example, one or both of the vacuum and argon lines (or
the combined vacuum/argon line) may be located on the pipe 28
before valve V2, or on the pipe 30 after the blower 26. In some
embodiments the evacuation operation 66 may be omitted, e.g. if the
flow of regeneration gas is high enough to efficiently push the
argon in the filter housing 24 out the exhaust 42. As another
contemplated variation, the blower could be placed on pipe 28 if it
can withstand exposure to low concentrations of pyrophoric
particulates.
[0033] As a further contemplated variation, in some embodiments the
regeneration gas may be delivered to the inlet side of the filter
22, and/or the exhaust may connect with the discharge side of the
filter 22. In a pore-type metal filter plate, the disclosed
approach of pushing the regeneration gas from the filter discharge
side 34 to the filter inlet side 32 and thence to the exhaust 42
has the advantage that particulates that are too large to pass
through the filter 22 (which are likely to be the particulates
"caught" by the filter 22) ensures that the filter 22 does not
block particulates from reaching the exhaust 42. However, if the
combustion of pyrophoric particulates "breaks up" the particulates
into smaller pieces that can pass through the filter 22, then the
regeneration gas may be flowed from the inlet side. As another
example, in the case of an electrostatic filter the electric power
can be removed from the filter during filter regeneration, and in
that case the regeneration gas can be fed into the filter from
either the inlet or outlet.
[0034] An advantage of the disclosed systems is that the filter
regeneration substantially extends the life of the filter 22.
Indeed, in some embodiments the expected lifetime of the filter 22
may be high enough that it is not considered a consumable item of
the system. Corollary benefits include reduced or eliminated
potential for fire or explosion, thus enhancing personnel and
equipment safety, as well as reduced waste (i.e., there is no spent
filter to be disposed of).
[0035] Another advantage is that recirculation of the gas defining
the controlled atmosphere greatly reduces the amount of gas that is
expended in a given process run. For example, in some spacer grid
laser welding applications it is expected that an argon flow rate
of about 300 liters per minute or higher will be employed. This
high flow rate is used to dissipate fumes (comprising at least in
part pyrophoric particulates) which would otherwise coat the
optical window 14 and occlude the laser beam 48. Recirculating and
simultaneously filtering the argon flow will greatly reduce the
argon consumption at these high flow rates.
[0036] The preferred embodiments have been illustrated and
described. Obviously, modifications and alterations will occur to
others upon reading and understanding the preceding detailed
description. It is intended that the invention be construed as
including all such modifications and alterations insofar as they
come within the scope of the appended claims or the equivalents
thereof.
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